Surface disinfection of patient care areas is a key factor in the constant battle to reduce or eliminate Hospital Acquired Infections (HAIs), also known in the art as nosocomial diseases or infections. Increased evidence published in scientific literature confirms that Clostridium difficile, MRSA, VRE, Acinetobacter baumannii, Bacillus subtilis var. niger, Bacillus anthracis Sterne, and influenza are transmitted via environmental surfaces and air. The problem has become so serious that many hospitals must close critical areas, such as operation theaters and intensive care units, to eradicate pathogens via terminal cleaning. HAIs contribute to rising health care costs and can lead to severe, if not lethal, effects on patients.
Surface disinfection of patient care areas can be performed by exposing surfaces to a dose (also referred to herein as “fluence”) of UV-C light, which is a form of electromagnetic intensity that is harmful to micro-organisms such as pathogens, viruses, and molds. Fluence is a measure of the quantity of light or other intensity impinging from all directions on the smallest possible three dimensional object. Fluence is often expressed in millijoules per square centimeter (mJ/cm2).
Ultraviolet germicidal irintensity (UVGI) is a sterilization method that uses ultraviolet (UV) intensity at a sufficiently short wavelength to break down micro-organisms. The short wavelength of UV-C is harmful to forms of life at the micro-organic level by destroying nucleic acids in these organisms so that their DNA and/or RNA chemical structure is disrupted by the UV intensity. The disruption prevents micro-organisms from replicating, thereby rendering them inactive and unable to cause infection. The primary mechanism of inactivation by UV is the creation of pyrimidine dimers, which are bonds formed between adjacent pairs of thymine or cytosine pyrimidines on the same DNA or RNA strand.
Low-pressure mercury lamps may be used for disinfection applications because they emit two narrow peak wavelengths of light at 185 nm and 254 nm, the latter peak being close to the wavelength where DNA and RNA experience maximum UV absorption (253.7 nm). The 185 nm emission causes disassociation of oxygen molecules to create ozone, a gas with a short half-life that is an air pollutant with harmful effects on respiratory systems. The EPA has designated a safe concentration of ozone concentration to be 0.05 ppm in air. Therefore, UV lamps that generate ozone are generally undesirable for use in closed areas.
A primary benefit of using UV light for disinfection is that it does not contain or create any residuals or byproducts, such as can occur with chemical methods of purification. In fact, UV light is sometimes used to remove residuals, and disinfection by-products, such as chlorine, peroxide, ozone, and trihalomethanes, that can result from other purification processes.
Different species of microorganisms require varying levels of UV-C exposure, but nearly all can be effectively inactivated with a fluence level of about 30 mJ/cm2 of surface area. Fluence levels of this intensity can achieve a 4-log reduction for most microorganisms, equivalent to a 99.99% reduction in the number of active organisms.
However, the effectiveness of UV surface disinfection is dependent on line-of-sight exposure of the micro-organisms to the UV source. Environments with obstacles that block the source are not as effective, and UV reflectance may be low and unreliable. In such an environment, such as a typical hospital room, effectiveness is then reliant on the placement of the source system so that line-of-sight is optimum for surface disinfection. The effectiveness of a surface disinfection unit (SDU) in such an environment depends on a number of factors, including the length of time a micro-organism is exposed to UV; power fluctuations of the UV source that impact the wavelength; the distance of the surface from the intensity source; the ambient temperature; the humidity of the air; the presence of particles in the air; the presence of dust and dirt on the lamp surface; the presence of particles that can protect the micro-organisms from UV; and a microorganism's ability to withstand UV during its exposure.
Various efforts have been made to improve line-of-sight exposure of the micro-organisms to the UV source. For example, a portable room disinfection unit employing a plurality of UV lamps on a single base unit has reportedly been available under the trade name TRU-D from Lumalier Corporation, Memphis, Tenn., USA. The tubular lamps are disposed vertically about a vertical axis and irradiate radially in different directions. A shortcoming of such a single-unit ultraviolet area sterilizer (UVAS) is that any equipment or appurtenances in the room, such as beds, tables, and chairs must necessarily create shadow areas which can be irradiated only at a reduced intensity by reflections.
U.S. Pat. Nos. 6,656,424 and 6,911,177 are both incorporated herein by reference in their entireties, and disclose a method and apparatus for a mobile or stationary automated UVAS. The UVAS is positioned in a room, such as an operating room or intensive care unit, where concern exists regarding the presence of pathogenic bacteria on environmental surfaces. For an initial interval after actuation, motion detectors sense movement, to assure that personnel have evacuated the space to be sterilized. Subsequently, UV-C generators, such as a bank of mercury bulbs, generate intense levels of UV-C. After the bulbs have reached a steady state of output, an array of UV-C sensors scan the room to determine the darkest area, or the area reflecting the lowest level of UV-C back to the sensors. A basic stamp contained in the device calculates the time required to obtain a bactericidal dose of UV-C reflected back from darkest area. The UVAS transmits the calculated dose of UV-C, as well as other monitoring information, to the remote control where it is displayed to the user. Once a bactericidal dose has been reflected to all the sensors, the unit notifies the user and shuts down. By relying on reflected doses rather than direct exposure, the UVAS purportedly is able to sterilize or sanitize all surfaces within the room that are within view of an exposed wall or ceiling.
As noted above for the TRU-D UVAS, a shortcoming of such a single-unit UVAS is that any equipment or appurtenances in the room, such as beds, tables, and chairs must necessarily create shadow areas which can be irradiated only at a reduced intensity by reflections. Further, auxiliary spaces, such a bathroom that commonly accompanies a hospital room, cannot be properly irradiated by a single UVAS, so a second UVAS is required. The patent references disclose an embodiment wherein a second UV lamp may be disposed apart from the UVAS, but powered and controlled by the UVAS, to assist in irradiating shadow areas of the UVAS. U.S. patent publication number US20120305787 A1 to Henson, application Ser. No. 13/153,408, published Dec. 6, 2012, is incorporated herein by reference in its entirety and discloses a UV surface disinfection system comprising a plurality of independently placeable and independently controllable surface disinfection units controlled by a single remote control console, each unit having a single ultraviolet lamp.
These real and proposed UV disinfection systems are employing increasingly complicated and expensive means to improve line-of-sight exposure of the micro-organisms to the UV source. In use, however, even the most advanced systems still require a user to largely guess whether they have placed the UVAS device(s) in the right location(s), and whether they have used them long enough at high enough power levels to sufficiently disinfect all the surfaces in a room, including hard-to-clean, shadowed and often overlooked high-touch surfaces such as electronic keyboards, remotes, and computers. What is needed is an inexpensive, easy-to-use apparatus, system, and method for evaluating the effectiveness of a given ultraviolet light disinfection of a room, which allows adjustments to be made to the location(s) and other parameters of the UV lamp(s) until the optimal treatment parameters for a given room can be established.